Variable output control for a fixed displacement pump

ABSTRACT

A device for adjusting the volume of fluid flow produced by a stroke of a piston pump includes a cylinder communicating with an outlet of the pump. A plunger displaces fluid from the cylinder to the outlet as the plunger moves in the cylinder. A lost motion piston moves in the cylinder. A fluid source supplies fluid to a first space in the cylinder located between the plunger and the piston. A port, through which fluid is supplied from the fluid source to a second space in the cylinder, is located above the piston such that the port is opened and closed by the piston. A stop establishes a maximum distance that the piston can move away from plunger toward the port without closing the port.

BACKGROUND OF THE INVENTION

This invention relates to adjusting the volume of fluid displaced by a stroke of a fluid pump. In particular, the invention relates to adjusting the starting load on an engine-pump assembly that supplies fluid for a hydraulic or pneumatic hybrid vehicle powertrain.

A hybrid powertrain motor vehicle may include various sources of power including an internal combustion engine, which drives a fluid pump, and sources of fluid pressure. Pressurized fluid from the pump and accumulators containing pressurized fluid supply hydraulic or pneumatic motors, which drive the vehicle wheels. Generally, such a hybrid powertrain includes a power accumulator containing fluid at relatively high pressure and a regen accumulator, in which kinetic energy of the vehicle, recovered from a brake regeneration system, is stored in the form of pressurized fluid. The accumulators and pump supply fluid to the motors at the wheels through a high pressure rail. Fluid exiting the fluid motors is returned to a reservoir, from which fluid is drawn to the pump inlet.

The stroke of the fixed displacement pump driven by the engine is a constant. The magnitude of pressure in the supply rail varies according to the degree to which the driver demands output power, the magnitude and occurrence of brake regeneration, the energy storage capacity of the accumulators, and other unpredictable factors including road conditions. When the engine is turned off, the magnitude of supply rail pressure is influenced by these conditions. Upon restarting the engine, the starting load on the engine and pump is affected by the magnitude of supply rail pressure.

Because there is little control over supply rail pressure and no control over the stroke of the fixed displacement pump, the engine may be required to start repeatedly against a large load, the pressure in the supply rail. Certain engines, such as a free piston engine or a conventional internal combustion engine operating with homogeneous combustion compression ignition, perform best when the amount of fuel supplied to the engine, the engine compression ratio, and the air-fuel ratio are controlled for each engine cycle within a close tolerance, even at engine startup. Such engines are susceptible to stalling if these parameters are not within narrow tolerances for each engine cycle.

To avoid these difficulties, it is preferred that such engines be started with idle fuel quantities so that the engine can respond to a demand for maximum power output after a large number of engine cycles have occurred after starting, rather than immediately upon startup. To accomplish this desired reduction in starting load, even when supply rail pressure is high, a technique is required to reduce the effective load placed on the engine for a period after engine startup, and as required for compatibility with operating conditions.

SUMMARY OF THE INVENTION

The present invention adjusts the effective stroke of a piston pump by adding a lost motion piston to the hydraulic system in order reduce the load placed on the engine and pump at startup. The lost motion piston permits a predetermined portion of the pump stroke to operate against low pressure in the pump cylinder through a spill port connected to the low pressure rail. Displacement of the piston eventually closes the spill port, allowing the residual portion of the pump stroke displace fluid from the cylinder to the high pressure rail.

The stroke of the lost motion piston is controlled by the position of a piston stop, which limits the displacement of the lost motion piston that occurs before the spill port is closed. The position of the piston stop is variable, so that the degree of lost motion is variable and controls the power output by the pump and the load on the engine at startup. These actions determine the magnitude of lost motion, i.e., extent to which the stroke of the pump is effective toward supplying flow to the system.

No high speed-high flow valves are needed to control the magnitude of fluid power delivered by the pump to the system. The magnitude of power loss is low compared to alternatives, and the design is compact.

A device for adjusting the volume of fluid flow produced by a stroke of a piston pump includes a cylinder communicating with an outlet of the pump. A plunger displaces fluid from the cylinder to the outlet as the plunger moves in the cylinder. A lost motion piston moves in the cylinder. A fluid source supplies fluid to a first space in the cylinder located between the plunger and the piston. A port, through which fluid is supplied from the fluid source to a second space in the cylinder, is located above the piston such that the port is opened and closed by the piston. A stop establishes a maximum distance that the piston can move away from plunger toward the port without closing the port.

Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a hybrid hydraulic system, to which the control of the present invention can be applied;

FIG. 2 is a schematic diagram of engine-pump assembly for supplying fluid to the hydraulic system;

FIG. 3 is a cross sectional view showing the pump cylinder and the control device for adjusting the effective stroke of the plunger;

FIGS. 4A-4D is a schematic diagram showing operation with the control set for the entire plunger stroke being effective;

FIGS. 5A-5D is a schematic diagram showing operation with the control set for approximately one-fourth of the plunger stroke being ineffective;

FIGS. 6A-6D is a schematic diagram showing operation with the control set for approximately one-half of the plunger stroke being ineffective; and

FIG. 7 is a schematic diagram showing an actuator for controlling the position of the stop.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the system illustrated in FIG. 1, a engine-pump 10 supplies hydraulic fluid from a low pressure line 11, which is hydraulically connected to a low-pressure accumulator 12, to a high pressure line or rail 13. The engine 10 is divided into multiple banks of cylinders 14, 16, 18, each cylinder being driveably connected to a hydraulic pump 15, 17, and 19. Check valves 20 are located in the fluid path between low-pressure line 11 and inlet of each pump 15, 17, and 19. Check valves 21 are located in the fluid path between high pressure line 13 and outlet of each pump. High pressure rail 13 is connected to a front pump/motor 22 and a rear pump/motor 26 so that they are supplied with pressure at substantially the same magnitude. The flow produced by engine 10 is directly proportional to the number of cylinders and the engine speed. Therefore, power output by the engine is closely related to line pressure, the pressure in rail 13.

A front hydraulic pump motor 22 is supplied with relatively high pressure fluid through a valve body 24, connected to high pressure line 13. Pump/motor 22 is driveably connected to the front wheels of a motor vehicle. Similarly, the rear hydraulic pump/motor 26 is supplied with high pressure hydraulic fluid through a valve body 28, connected to high pressure rail 13. The rear wheels of the motor vehicle are driven in rotation by pump/motor 26. The front and rear pump/motors 22, 26 are variable displacement hydraulic pumps, each pump having a maximum displacement or volumetric flow rate.

When an increase of power must be delivered to the front wheels and rear wheels through the pump/motors 22, 26 while the pumps are operating at maximum displacement, the pressure supply to the pump motors must be increased in order to increase the output power from the pump/motors. During normal operation the pump/motors 22, 26 generate torque by fluid flow from high pressure rail 13 to low pressure line 11. When the wheel brakes are braking the vehicle, the direction of torque and direction of fluid flow are reversed. Disregarding losses, torque is proportional to the product of displacement and pressure difference. Flow rate is proportional to the product of speed and displacement.

The hydraulic fluid outlet side of the engine 10, through which rail 13 is supplied, is connected to an engine accumulator 30, which buffers or attenuates hydraulic pressure pulses produced by variations in engine speed and its inertia. A high pressure or power mode accumulator 32 communicates with rail 13 through a valve 34. A spring 36 biases the valve 34 to the position shown in FIG. 1, where check valve 38 opens and closes the hydraulic connection between accumulator 32 and rail 13 depending on that pressure differential across valve 34. When actuated, solenoid 40 overcomes the effect of spring 36 and moves the valve to a second state where a connection between accumulator 32 and rail 13 is open through the valve.

A brake regeneration accumulator 42 stores energy recovered during the process of braking the drive wheels of the motor vehicle and stores that energy in the form of relatively high pressure hydraulic fluid. Accumulator 42 is connected to and disconnected from line pressure in rail 13 through a valve 44 in accordance with the state of two control solenoids 46, 48.

The outlet side of the front pump/motor 22 is connected through line 50 and check valve 52 to a heat exchanger 54, filter 56 and a case drain reservoir 58. Similarly, the outlet side of the rear hydraulic pump/motor 26 is connected through line 60 to the case drain reservoir 58. A recovery pump 62 draws hydraulic fluid from the reservoir 58 and supplies fluid to the system through a check valve 64 and line 66. Line 66 mutually connects the valve blocks 24, 28, and accumulator 12 is connected to line 66, through which the inlet side of the hydraulic pumps 15, 17, 19 are supplied.

Referring now to FIG. 2, the engine pump 10 includes a first cylinder 80 in which a first inner piston 82 and first outer piston 84 reciprocate along the axis 86. Similarly, a second cylinder 88 contains a second inner piston 90 and an outer piston 92 which reciprocates along the axis 86. The inner pistons 82, 90 connected by bolts 94, 96 to a hydraulic plunger 98, which reciprocates with the piston within a hydraulic cylinder 100. Hydraulic fluid at relatively low pressure is supplied to a cylinder 100 from a low pressure rail 66 through a check valve 102, which permits flow to cylinder 100 when the pressure in rail 66 is greater than the pressure in the cylinder, and prevents flow from rail 66 to the cylinder by closing communication between the cylinder and the rail 66. Similarly, plunger 108 forces hydraulic fluid from cylinder 100 through a check valve 104 to a high pressure rail 13. Check valve 104 prevents flow from rail 13 to cylinder 100.

The details of lost motion device are shown in FIG. 3. The plunger 98 of the engine-pump assembly 10 reciprocates within cylinder 100, from which hydraulic fluid is displaced through check valve 104 to an outlet passage 106, which communicates with high pressure rail 13. Fluid enters the pump from the low pressure rail 66 through an inlet passage 108 and check valve 102.

A lost motion piston 110 is supported on a stem 112 for movement within the cylinder. The stem has a head 114, for contacting a stop surface 116, which limits downward movement of piston 110 but permits upward movement of the piston stem 112 through the cylinder head 118. A spill port or low pressure port 120 communicates rail 66 with a portion of cylinder 100 located between the cylinder head 118 and piston 110.

In operation, FIGS. 4A-4C shows the control disposed such that the entire stroke of the plunger 98 is effective to displace fluid from the cylinder 100, i.e. to produce a full stroke. Referring to FIG. 4A, stop 116 is located at a position such that spill port 120 is closed by the flanges 122 of the piston 110, and plunger 98 is at its bottom dead center (BDC) position. In FIG. 4B, plunger 98 has moved upward by the reciprocation of the pistons, and check valve 104 has been opened by the pressure in cylinder 100. Lost motion piston 110 does not move upward because fluid is trapped between the cylinder head 118 and piston 110. In FIG. 4C the plunger 98 has moved further upward to its top dead center (TDC) position, the extremity of its travel in the cylinder. As the pistons reciprocate, plunger 98 is forced downward, check valve 104 closes, check valve 102 opens, and fluid at low pressure enters cylinder 100.

Turning now to FIGS. 5A-5D, the control stop 116 is located lower than its position of FIGS. 4A-4C to a position where approximately one-fourth of the stroke of plunger 98 ineffective in displacing fluid from cylinder 110. In FIG. 5A, the cylinder 100 is again filled through check valve 102 with fluid from the low pressure rail 66. The head 114 on the piston 110 is contacting stop 116, but piston 110 does not close the spill port 120. As plunger 98 moves upward within the cylinder 100 to the position of FIG. 5B, the spill port 120 becomes covered by piston 110, thereby entrapping hydraulic fluid within the space 124 between the cylinder head 118 and piston 110. As piston 110 moves upward to the position of FIG. B, the head 114 moves away from stop 116, but high pressure check valve 104 remains closed because the spill port 120 is open to rail 66. Movement of the plunger 98 from the position of FIG. 5A to that of FIG. 5B does not displace fluid from the cylinder to the high pressure rail 13. Therefore, this portion of the plunger stroke is ineffective toward displacing fluid from the pump.

As plunger 98 moves further upward to the position of FIG. 5C, the increased pressure in the cylinder opens check valve 104 after port 120 closes. The residual portion of the stroke of plunger 38 displaces fluid from cylinder 100 to the high pressure rail 13. In FIG. 5D, plunger 38 has moved to the upper end of its travel, spill port 120 remains closed, and plunger 38 begins to move downward. This movement of the plunger 98 closes check valve 104, opens check valve 102, and draws low pressure fluid into cylinder 100 through valve 102 from rail 66.

FIGS. 6A-6D illustrate the control disposed to cancel approximately half of the stroke of plunger 98. FIG. 6A shows plunger 98 at the lower end of its displacement. Stop 116 has moved still further downward to a position where head 114 resting on the stop permits piston 110 to extend further downward into cylinder 110 than the position of FIG. 5A. Port 120 is fully open to rail 66. In FIG. 6B, plunger 98 has moved upward from its BDC position approximately one-half of its stroke. In this position, cylinder 110 closes spill port 120. During displacement of plunger 98 from the position of FIG. 6A to the position of FIG. 6B, little hydraulic fluid has been displaced from the cylinder 100 by the plunger because the high pressure check valve 104 remains closed due to differential pressure across that check valve. When plunger 98 moves further upward within the cylinder, piston 110 keeps spill port 120 closed, but does not move upward due to the entrapped fluid in space 124. But fluid is displaced from cylinder 100 through check valve 104 and the outlet 106 of the high pressure rail 13. FIG. 6D shows plunger 38 at the upper end of its displacement.

The position of the stop 116 can be controlled electronically in response to a signal from an electronic controller. The signal for actuates a stepper motor or a solenoid as shown in FIGS. 7A and 7B. The actuator causes actuating arm 132 to pivot around fulcrum 134, thereby moving the stop 116 upward and downward in relation to the head of the cylinder in accordance with the extent to which the solenoid is extended or retracted. Alternatively, an inclined plane moved by the actuator across the stop 114 adjusts the position of the stop, thereby adjusting the effective displacement of the pump.

In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope. 

1. Apparatus for adjusting the volume of fluid flow produced by a stroke of a piston pump, establishing the volume of fluid flow produced by a stroke of a fluid pump, comprising: a cylinder communicating with an outlet of the pump; a plunger for displacing fluid from the cylinder to the outlet as the plunger moves in the cylinder; a piston moveable in the cylinder; a fluid source for supplying fluid to the cylinder between the plunger and the piston; a port communicating with the cylinder and fluid source, opened and closed by the piston; and a stop for establishing a maximum distance that the piston can move away from plunger toward the port without closing the port.
 2. The apparatus of claim 1, further comprising: a first check valve for alternately opening and closing communication between the fluid source and the cylinder; and a second check valve for alternately opening and closing communication between the cylinder and the outlet.
 3. The apparatus of claim 1, further comprising: a first check valve for alternately opening and closing communication between the fluid source and the cylinder; a second check valve for alternately opening and closing communication between the outlet and the cylinder; wherein the first check valve opens and closes in response to differential pressure across the first check valve; and the second check valve opens and closes in response to differential pressure across second check valve.
 4. The apparatus of claim 1, wherein the cylinder includes a head that closes the second against entry and exit of fluid except through the port.
 5. The apparatus of claim 1, further comprising: an actuator for changing the location of the stop, thereby adjusting a distance that the piston can move away from the port.
 6. The apparatus of claim 1, further comprising: an actuator for changing the location of the stop, thereby adjusting a distance that the piston can move in the cylinder before closing the port.
 7. The apparatus of claim 1, wherein the second space has a length along the cylinder ort is closed that varies as the piston moves in the cylinder.
 8. The apparatus of claim 1, wherein the stop limits the distance that the piston can from the port toward the plunger.
 9. Apparatus for adjusting the volume of fluid flow produced by a stroke of a piston pump, comprising: a cylinder communicating with an outlet of the pump, including an axial end closed by a head; a plunger for displacing fluid from the cylinder to the outlet as the plunger moves in the cylinder; a piston moveable in the cylinder; a fluid source for supplying fluid to the cylinder between the plunger and the piston; a port communicating with the cylinder, opened and closed by the piston; and a stop located for contact with the piston for limiting movement of the piston toward the plunger, and establishing a distance that the piston can move away from plunger toward the port without closing the port.
 10. The system of claim 9, further comprising: an engine for producing linear reciprocating output, said engine output being driveably connected to the plunger.
 11. The system of claim 9, further comprising: a free piston engine producing linear reciprocating output, said engine output being driveably connected to the plunger.
 12. The system of claim 9, wherein the piston is moves in the cylinder in response to differential pressure across the piston.
 13. The apparatus of claim 9, further comprising: a first check valve for alternately opening and closing communication between the fluid source and the cylinder; and a second check valve for alternately opening and closing communication between the cylinder and the outlet.
 14. The apparatus of claim 9, further comprising: a first check valve for alternately opening and closing communication between the fluid source and the cylinder; a second check valve for alternately opening and closing communication between the cylinder and the outlet; wherein the first check valve opens and closes in response to differential pressure across the first check valve; and the second check valve opens and closes in response to differential pressure across second check valve.
 15. The apparatus of claim 9, wherein the cylinder includes a head that closes the second against entry and exit of fluid except through the port.
 16. The apparatus of claim 9, further comprising: an actuator for changing the location of the stop, thereby adjusting a distance that the piston can move away from the port.
 17. The apparatus of claim 9, further comprising: an actuator for changing the location of the stop, thereby adjusting a distance that the piston can move in the cylinder before closing the port.
 18. The apparatus of claim 9, wherein the second space has a length along the cylinder ort is closed that varies as the piston moves in the cylinder.
 19. The apparatus of claim 9, wherein the stop limits the distance that the piston can from the port toward the plunger.
 20. A method for adjusting a portion of the stroke of a piston pump that is effective in displacing fluid from the pump, comprising the steps of: providing a cylinder supplied with fluid, and a plunger displaceable in the cylinder for pumping fluid from the cylinder; providing a spill port communicating with the cylinder; locating a piston at a first position in the cylinder between the spill port and the plunger, the piston being displaceable in response to displacement of the plunger; establishing a length of piston displacement between the first position and a second position where the piston closes the spill port; and displacing the plunger in the cylinder.
 21. The method of claim 21, further comprising the step of adjusting the length of piston displacement between the first position and a second position.
 22. The method of claim 21, further comprising the step of: providing a stop contacted by the piston for limiting said length of piston displacement.
 23. The method of claim 21, further comprising the steps of; providing a stop contacted by the piston for limiting said length of piston displacement; and adjusting said length of piston displacement between the first position and a second position. 